The present invention refers to an apparatus for clamping a work piece in a well defined position within the operating area of a machine tool, comprising a chuck member adapted to be fixed within the operating area of the machine tool, a work piece carrier adapted to be fixed to the chuck member and to be clamped thereto, and a clamping mechanism for clamping the workpiece carrier to the chuck member.
Such an apparatus, well known in the art, primarily serves for clamping a work piece to be machined in the operating area of a machine tool with very high accuracy. It is particularly important that also the repetitive accuracy is ensured. In other words, the work piece received on the work piece carrier has to be clamped subsequently many times on a chuck member adapted to the work piece carrier and shall thereby have always a precisely defined position in X-direction, in Y-direction, in Z-direction and also regarding the angular orientation around the Z-axis, for example in circumstances if the work piece carrier bearing the work piece to be machined has to be clamped in different machine tools that subsequently perform different machining operations and are each equipped with an identical chuck member, or in measuring and test stations equipped with the same chuck member as well.
Such an apparatus is disclosed, for example, in the European Patent Nr. 0,255,042. That apparatus comprises two pairs of positioning strip members towering above the surface of the chuck member, equipped with contact surfaces for the orientation of the work piece carrier in X- and Y-directions. Moreover, four pins are provided also towering above the surface of the chuck member. These pins are responsible for defining the Z-position of the work piece carrier. The matching work piece carrier comprises a plane surface adapted to rest against the afore mentioned pins provided on the chuck member. Furthermore, the surface of the work piece carrier is provided with two pairs of grooves in a layout corresponding to the one of the afore mentioned positioning strip members. The grooves have flexible lips that are intended to rest against the contact surfaces of the afore mentioned strip members of the chuck member. Finally, the work piece carrier has a central aperture for receiving a pulling bolt member by means of which the clamping force required to maintain the defined position between work piece carrier and chuck member is transferred. Thereby, the chuck member comprises a centrally located ball lock mechanism cooperating with that pulling bolt member.
A disadvantage of such a known apparatus may be seen in the fact that it is relatively unstable, particularly if bigger and heavier, respectively, work pieces have to be machined. Thus, it cannot resist high tilting momenta or torque forces that can occur especially in the case of cutting operations. An increase of the size of the apparatus that would also increase the stability is not desired in many cases due to limited space availability.
Thus, it is an object of the present invention to provide an apparatus for clamping a work piece in a well defined position within the operating area of a machine tool in which the work piece carrier clamped to the chuck member and, thereby, the work piece to be machined has a substantially increased resistance against tilting momenta and torque forces, simultaneously avoiding the danger that the work piece carrier and, thereby, the work piece is displaced relative to the chuck member, all this by maintaining the desired small size and a very high accuracy as far as the positioning of the work piece carrier relative to the chuck member is concerned, particularly also in the case of repetitive clamping, as explained herein before.
In order to meet these and other objects, the invention provides an apparatus for clamping a work piece in a well defined position within the operating area of a machine tool, comprising a chuck member adapted to be fixed within the operating area of the machine tool, a work piece carrier adapted to be fixed to the chuck member and to be clamped thereto, and a clamping mechanism for clamping the workpiece carrier to the chuck member and adapted to be switched from a released condition to a clamping condition and vice versa.
The chuck member comprises first positioning members and the work piece carrier comprises second positioning members. The first and second positioning members cooperate such as to define the position of the work piece carrier relative to the chuck member along three coordinate axes each running perpendicular to each other, i.e. the X-axis, the Y-axis and the Z-axis, as well as with regard to the angular orientation around the Z-axis.
The clamping mechanism thereby fixes the work piece carrier to the chuck member once it is switched to the clamping condition to maintain the defined position.
The first positioning members are constituted by conical centering pins and the second positioning members are constituted by recesses in the shape of a two-stage groove. The groove has two shoulders whose edges protrude towards the interior of the groove. The mutual distance of these edges is somewhat less than the width of the conical centering pins, measured between those locations that touch these edges once the work piece carrier is clamped to the chuck member.
In order to even further increase the desired high resistance against unintentional positional changes caused by tilting and torque momenta occurring under heavy load, it is provided in a preferred embodiment that the centering pins are evenly distributed along the edge of the top surface of the chuck member, whereby at least the peripherally opposite lateral surfaces of the centering pins are inclined with regard to the Z-axis of the apparatus. Moreover, the first positioning members further comprise elevated surface portions located on the top surface of the chuck member and extending up to the edge thereof.
An even still further increased resistance to withstand high torque forces can be achieved if the recesses are machined into a shoulder provided in an upper portion of the work piece carrier, whereby the shoulder protrudes towards the interior of the hollow cylindrical work piece carrier, the location of the recesses corresponding to the location of the centering pins provided on the chuck member.